Generally, expandable particles comprising composite resin of polyolefin-based resin and polystyrene-based resin (may be simply referred to as expandable composite resin particles) are obtained by impregnating composite resin particles (may be simply referred to as resin particles) with a volatile blowing agent. In addition, it is known that water is included in the expandable composite resin particles in order to improve the moldability of expanded molded articles (see, for example, Japanese Examined Patent Publication No. HEI 6(1994)-104746 (Patent Document 1)).
In Patent Document 1, the expandable composite resin particles contain 0.5 to 1.5% by weight of water, and the volatile blowing agent used in Examples is butane (n-butane: 70% and isobutane: 30%).